by Farsi, Deema, M.S., Tufts University School of Dental Medicine, 2009, 37; 1464253

Abstract (Summary)

Background. Over the long course of research, Gram positive bacteria associated with dental caries and Gram negative bacteria associated with periodontal disease have both shown sensitivity to triclosan (TCS). Research has indicated that resistance to triclosan can develop in several bacterial species including Escherichia coli. However, clinical studies have concluded that the daily use of toothpastes containing 0.3% triclosan was not associated with resistance development in periodontal-disease causing bacteria. No studies, however could be found that attempted to induce triclosan-resistance in Porphyromonas gingivalis, Prevotella intermedia and Tannerella forsythia in vitro.

Aims. Detect the sensitivity of P. gingivalis, P. intermedia and T. forsythia to triclosan, determine whether resistant strains develop for each species, and if so, determine the concentration of triclosan which induces resistance.

Materials and Methods. E coli AG100 triclosan-sensitive (S) and E coli AGT11 triclosan-resistant (R) were used as control strains. P. gingivalis FDC 381, P. intermedia ATCC 25611, T. forsythia FDC 338 (ATCC 43037) were used as test species. Inoculae were prepared by harvesting cells from agar into prereduced anaerobically sterilized (PRAS) Ringer's salt solution. Cell concentrations were estimated by reading the optical density (OD) of inoculae at 600nm (OD 1 equivalent to 109 cells). Ten–fold dilutions of bacterial cells were prepared, and selected concentrations were plated on the test and control plates. The basal medium for triclosan testing contained Trypicase Soy, Brain Heart infusion and yeast extract agars supplemented with hemin and menadione for P. gingivalis and P. intermedia, and with N-acetyl muramic acid for T. forsythia. Triclosan containing medium was the same as basal medium but supplemented with different concentrations of Triclosan diluted in ethanol at 10/100x concentration.

Results. E. coli R grew on all triclosan-containing plates, demonstrating resistance to triclosan. E coli S did not grow in 7 days in any TCS containing agar. P. intermedia was sensitive at 2 μg/ml triclosan. P. gingivalis was sensitive at 2 μg/mg triclosan. T. forsythia was sensitive at 1.66 μg/ml triclosan. Resistant colonies developed after prolonged incubation for E coli S and P. intermedia which was transient and unstable. No resistance developed for P. gingivalis or T. forsythia.

Conclusion. A system to evaluate sensitivity to triclosan was adapted for these fastidious anaerobic periodontal pathogens. Low levels of transient resistance to triclosan was observed for P. intermedia , but not for P. gingivalis or T. forsythia. The results of this research support the use of triclosan in the commercially available dental products to control periodontal disease.

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